Process for the currentless deposition of copper-tin layers



United States Patent 0 33,648 US. Cl. 117-130 Int. Cl. C23c 3/00,- B44d 1/34 The invention relates to a process for the deposition of copper-tin layers on iron and steel surfaces without the use of an electric current and, more particularly, to the deposition of such layers in the presence of polyaminopolycarboxylic acids, whereby stable layers are obtained having a pleasant bronze color and good properties by cold shaping of the metal thus plated, e.g., upon the drawing of wires therefrom.

Solutions have been proposed for the currentless deposition of copper-tin layers which contain, in acid solution, copper salts and tin-II-salts. However, these solutions are quite sensitive to variations in their concentration and readily decompose with precipitation of metastannic acid. Moreover, the deposits or coatings frequently are spongy and lack proper adhesion to the substrate.

It now has been found that coating layers of good adhesion to iron and steel are obtained by treating these metals with solutions in a pH range of 0.5 to 6 and containing sulfates of copper and of bivalent tin in weight proportions of CuSO .5H O:SnSO =2:l to 1:2 plus 0.01 to 0.15 weight percent of a polyaminopolycarboxylic acid. It has been established that these solutions, within the limits of concentration named, are stable and that no metastannic acid precipitates. Thus, the disadvantages of the known processes are avoided by the method according to the invention.

It is a requirement that the solutions contain the coating or plating metals in the form of their sulfates because other anions, such as the chloride or nitrate, interfere with their deposit on the iron or steel. The proportions of copper to tin may vary within the limits given above. By this variation, the color of the copper-tin plating is influenced and varies from a very light to a dark bronze tone, an increase in the amount of copper leading to darker hues.

The concentration of the copper sulfate, calculated as CuSO .5H O, opportunely is held between 1 and 20 grams per liter-(g./l.), and preferably between 5 and 15 g./1. The concentration of the tin-II-sulfate follows from the proportion of CuSO .5H O:SnSO =2:1 to 1:2 and the desired bronze color.

The solution can be controlled by determining the copper content. It has been found advantageous, in order not to prolong the plating times unnecessarily, to replenish the solution after it has reached approximately of its original copper quantity. Replenishment of the solution can be carried out by adding the proportionate mixture of the solid components. The composition of this mixture opportunely is chosen so that the components are present in the same proportion as originally present. This procedure can be repeated several times because 8 Claims the activity of such a solution is largely independent of 3,432,337 Patented Mar. 11, 1969 metrical quantities of the polyaminopolycarboxylic acid used. The addition of these acids is in amounts of 0.01 to 0.14 weight percent, and preferably 0.04 to 0.12 percent. Suitable polyamino-polycarboxylic acids are ethylenediaminotetraacetic acid (EDTA) and those acids which resemble EDTA in the properties, for instance diethylenetriaminopentaacetic acid, N-(Z-hydroxycyclohexyl)ethylenediaminotriacetic acid and ethyleneglycol-bis-(betaaminoethylether)-tetraacetic acid. The acids also can be employed in the form of their salts. Other compounds which resemble the polyaminopolycarboxylic acids regarding their capability of forming complexes, e.g., tartaric acid, citric acid or gluconic acid, do not give equally favorable effects.

The solutions according to the invention are employed in a pH range of 0.5 to 6. It has been found advantageous to add thereto 0.5 to 30 g./l., and preferably 2.5 to 15 g./l., of concentrated sulfuric acid (d. 1.84). When the solution is replenished as described above, further addition of sulfuric acid is not required.

The solutions are employed for plating of iron and steel at temperatures ranging from 10 to 40 C. At room temperature, it requires approximately 1 to 6 minutes to deposit a layer of 12,u. thickness. The plating time is dependent upon the temperature and the concentration of the solution. Therefore, plating at too low a temperature is not recommended, nor is a too far-reaching use of the solution.

After the desired copper-tin coating has been deposited, the metal surfaces thus treated are rinsed with water for the removal of adhering solution. It does not matter whether the rinse water is hot or cold.

It is necessary to clean the iron and steel surfaces prior to plating with the copper-tin layer. The cleansing step can be carried out in the conventional manner, using alkaline, acidic, neutral or emulsion type cleansers, depending upon the degree of contamination of the surfaces, and is of no influence on the ensuing plating. In order to activate the surfaces after degreasing, a short-time etching with sulfuric or hydrochloric acid has been found beneficial, but not a requirement.

The invention now will be further explained by the following examples. However, it should be understood that these are merely given by way of illustration, not of limitation, and that numerous changes may be made in the details without departing from the spirit and the scope of the invention as hereinafter claimed.

EXAMPLE 1 An aqueous solution was prepared containing 7.15 g./l. CuSO .5H O, 10 g./l. SnSO 0.85 g./l. ethylendiaminotetraacetic acid, and 5.6 g./l. H (d. 1.84). This solution was used to coat well degreased iron wire. The bath temperature was 25 C., and the time of action 4 minutes. During that time, a well adhering light bronze colored layer of 1-2 had formed on the surfaces of the wire which then was rinsed with cold water.

After approximately /3 of the copper present had been spent, the solution was replenished to its original concentration by the addition of a solid powder of the following composition: 39.7 weight percent CuSO .5H O; 55.5% SnSO and 4.8% EDTA.

EXAMPLE 2 An aqueous solution containing 15 g./l. CuSO .5H O; 10.0 g./l. SnSO 1.0 g./l. EDTA and 2.5 g./l. H SO (d. 1.84) was used as bath for the plating of steel wire which previously had been degreased and etched with sulfuric acid The bath temperature was 30' C., the time of exposure 3 minutes; and a 1-2 thick bronze-colored and well adhering copper-tin coating was obtained. The

3 wires thus treated exhibited good properties upon drawing. They were rinsed with water at 30 C.

The solution was brought back to full strength repeatedly by adding thereto a solid powder composed of 56.6 weight percent CuSO .5H O; 385% SnSO and 3.9% EDTA. The efficiency of the solution was not decreased thereby.

EXAMPLE 3 Well-adhering copper-tin platings of 1-2 1. thickness and having good quality upon cold shaping of the substrate were applied to iron and steel surfaces, respectively, with aqueous solutions as named below at temperatures of 15 to 35 C. within 2 to 6 minutes.

g./l. CuSO .5H O 12 SnSO 12 EDTA 1.0 H 50 (d. 1.84) 15 The coatings were bronze-colored.

g./l. CuSO .5H O 13.6 SnSO 8 N- Z-hydroxycyclohexyl -ethylenediaminotriacetic acid 1.0 H2804 (d. 1.84) 5 The copper-tin layer had a dark bronze color.

g./l. CuSO .5H O 8.5 SnSO ethylenoglycol-bisbetaaminoethylether) tetraacetic acid 0.9 H 80, (d. 1.84) 12.5

The plating had a very light bronze color.

g./l. CUSO4-SHzO 5 SnSO, 8.5 EDTA 0.5 H 50 (d. 1.84) 4 The coating had a light bronze color.

g./l. CUSO4-SH2O 8 511804 8.5 EDTA 1.2

The copper-tin layer had a bronze color.

g./l. CuSO .5H O 7.5 SnSO, 10.5 5,;8-diaminodiethylethertetraacetic acid 0.8 H 50 (d. 1.84) 2.5

The plating had a light bronze color.

The solutions could be replenished with the corresponding solid mixtures of CuSO .5H O, SnSO, and polyaminopolycarboxylic acid.

What is claimed is:

1. A process for the currentless deposition of copper-tin layers on the surfaces of iron and steel which comprises treating said surfaces at temperatures ranging from substantially 10 to substantially 40 C. for approximately 1 to 6 minutes with an aqueous solution of CuSO .5H O and SnSO, in weight proportions of 2:1 to 1:2, said solution further containing 0.01 to 0.15 weight percent of a polyaminopolycarboxylic acid, and having a pH range of 0.5 to 6; followed by rinsing the surfaces with water.

2. A process for the currentless deposition of coppertin layers on the surfaces of iron and steel which comprises treating said surfaces at temperatures ranging from substantially 10 to substantially 40 C. for approximately 1 to 6 minutes with an aqueous solution of CuSO .5H O and SnSO in weight proportions of 2:1 to 1:2, said solution containing 1 to 20 g./l. CuSO .5H O, and further containing 0.01 to 0.15 weight percent of a polyaminopolycarboxylic acid and having a pH range of 0.5 to 6; followed by rinsing the surfaces with water.

3. The process as defined in claim 2, wherein said polyaminopolycarboxylic acid is selected from the group consisting of ethylenediaminotetraacetic acid, diethylenetriaminopentaacetic acid, N-(2-hydroxycyclohexyl)-ethylene-diaminotriacetic acid ethylenglycol-bis (betaaminoethylethertetraacetic acid, and flfi-diaminodiethyltetraacetic acid.

4. The process as defined in claim 2, wherein said solution contains substantially 0.5 to 30 g./l. concentrated sulfuric acid.

5. A plating solution for the currentless deposition of a copper-tin layer on steel and iron surfaces which comprises an aqueous solution containing CuSO .5H O and SnSO in weight proportions of 1:2 to 2:1, and 0.01 to 0.15 Weight percent of a polyaminopolycarboxylic acid, said solution having a pH range of substantially 0.5 to 6.

6. A plating solution for the currentless deposition of a copper-tin layer on steel and iron surfaces which comprises an aqueous solution of CuSO .5H O and SnSO in weight proportions of 2:1 to 1:2, said solution containing 1 to 20 g./l. CuSO .5H O, and further containing 0.01 to 0.15 weight percent of a polyaminopolycarboxylic acid, said solution ranging in pH from substantially 0.5 to substantially 6.

7. The plating solution as defined in claim 6, wherein said polyamino-polycarboxylic acid is selected from the group consisting of ethylenediaminotetraacetic acid, diethylenetriaminopentaacetic acid, N-(Z-hydroxycyclohexyl) ethylenediaminotriacetic, ethyleneglycol-bis (betaminoethylether)-tetraacetic acid, and B, B'-diaminodiethyltetraacetic acid.

8. The plating solution as defined in claim 6, further containing substantially 0.5 to 30 g./l. concentrated sulfuric acid.

References Cited UNITED STATES PATENTS 510,376 '12/1893 'Bertrand 106--l 3,075,856 1/1963 Lukes 117130 X 3,346,404 10/1967 Gardner et a1. 117130 X OTHER REFERENCES Camp et al.: The Making, Shaping and Treating of Steel, p. 1062, 6th ed., 1951.

Narcus: Metal Finishing, vol. 50, N0. 3, March 1952, p. 61.

RALPH S. KENDALL, Primary Examiner.

US. Cl. X.R. 

1. A PROCESS FOR THE CURRENTLESS DEPOSITION OF COPPER-TIN LAYERS ON THE SURFACE OF IRON AND STEEL WHICH COMPRISES TREATING SAID SURFACES AT TEMPERATURES RANGING FROM SUBSTANTIALLY 10 TO SUBSTANTIALLY 40*C. FOR APPROXIMATELY 1 TO 6 MINUTES WITH AN AQUEOUS SOLLUTION OF CUSO4.5H2O AND SNSO4 IN WEIGHT PROPORTIONS OF 2:1 TO 1:2, SAID SOLUTION FURTHER CONTAINING 0.01 TO 0.15 WEIGHT PERCENT OF A POLYAMINOPOLYCARBOXYLIC ACID, AND HAVING A PH RANGE OF 0.5 TO 6; FOLLOWED BY RINSING THE SURFACES WITH WATER. 